This application is a national phase of PCT/FR99/02034 which was filed on Aug. 24, 1999, and was not published in English.
The invention relates to a process for collective packaging of a plurality of components initially formed in a same substrate. In particular, packaging may include individualization of parts of the substrate, called modules, each comprising at least one component. Packaging may also include making electrical contacts on the component(s), making thermal contacts for the dissipation of heat produced by the component(s), and packaging of components.
Furthermore, an electronic component is an individual component, and particularly an active component such as a transistor or an assembly formed of a plurality of components such as an amplification stage.
The invention is used in applications in many electronics fields and particularly for the packaging of electronic power components, that requires thermal contact between components or the substrate and dissipation heat sinks.
A number of techniques are known for transferring a first substrate comprising a number of components onto a second substrate, essentially acting as a connection intermediary between connection pads and input/output terminals of components on the first substrate.
In particular, a xe2x80x9cflip-chipxe2x80x9d technique consisting of hybridisation by meltable material is known. According to this technique, connection strips of the substrates to be hybridised placed facing each other are electrically and mechanically connected through bushings made of meltable material welded collectively onto the connection strips.
The hybridisation technique using meltable material may be used particularly to add a plurality of electronic chips each comprising one or several components, onto a large support substrate. However in this type of application, all chips have to be positioned individually on the support substrate before starting the heat treatment to melt the meltable material in the bushings for collective soldering.
Individual positioning of the chips is an expensive step that can prevent industrial manufacturing of assemblies from being cost effective.
The hybridisation technique using meltable material can also be used for the interconnection of a plurality of stacked substrates connected electrically by bushings formed on their main faces opposite each other.
Contacts and connections to the outside of this type of stack are formed on the main free outside faces. The existence of large number of input/output terminals on the main free faces forms a handicap to installation of heat sinks designed for power components.
The document xe2x80x9cSmart Power ICS Technologies and Applicationsxe2x80x9dxe2x80x94B. Murani, F. Bertotti, G. A. Vignolaxe2x80x94Spinger Chap. 13 contains an illustration of the state of the art described above.
The purpose of the invention is to propose a process for packaging and particularly for making electrical contacts for components formed on a substrate without the limitations of the techniques described above.
One purpose in particular is to propose a process for collectively processing a large number of components initially formed on a same substrate, and consequently adapted to industrial use.
Another purpose is to propose a process for reconciling requirements to make electrical contacts on a large number of input/output terminals and efficient thermal contact for dissipation of heat from power components.
More precisely, in order to achieve these purposes, the objective of the invention is a process for collective packaging of a plurality of components formed in a first substrate board and separated from each other by separation strips, each component comprising at least one contact pad flush with a first surface of the said first board. The process according to the invention comprises the following steps in sequence:
a) formation of a depression in at least one separation strip contiguous to the said component, in the first board, for each component,
b) formation of conducting tracks on a second substrate board, each track being associated with the contact pads of components on the first board, each of the conducting tracks associated with the contact pads of a component on the first board extending onto a xe2x80x9cconnectionxe2x80x9d strip, the connection strip being arranged to coincide with the depression contiguous with the said component on the first substrate board, when the first and second substrate boards are assembled,
c) assembly of the first and second substrate boards so as to bring the contact pads of the components of the first board into electrical contact with the corresponding tracks on the second board, and to make each connection strip on the second board coincide with a corresponding depression on the first board,
d) cutting out the first board by the formation of xe2x80x9cproximalxe2x80x9d trenches around the components, the proximal trenches opening up into the said depressions in the separation strips, and cutting out the second board around the components by the formation of xe2x80x9cdistalxe2x80x9d trenches, further away from the components than the proximal trenches in regions comprising connection strips, in order to allow the connection strips on the second board to project at least partially beyond at least one edge of the first board, the first and second cut outs being used to individualise the modules each formed of a portion of the first board comprising at least one component and one portion of the second board.
With the process according to the invention, the board interconnection and assembly operation is collective until the modules are cut out. Consequently, it is suitable for inexpensive industrial implementation.
Furthermore, since the connection strip of the second substrate board projects laterally beyond the first board, it is possible to make electrical connections on this strip without taking up space on the main faces of the substrate boards. These faces can then be used for other contact terminals, if any, or be fitted with heat sinks to dissipate heat produced by power components integrated in the substrate boards, if any.
For example, the substrate boards can be cut out in step d) by sawing. They can also be cut using a water jet and/or by laser. Etching techniques may also be used using reactive ions, particularly in combination with other cutting techniques. Etching may be used to increase the precision and finish quality of the cut.
The first and second boards may be cut at the same time by using a saw with offset blades or a step-shaped saw blade.
During step a) of the process, the electrical connection between contact pads on the first substrate board and conducting tracks on the second substrate board may for example be made using bushings of meltable material using the xe2x80x9cflip-chipxe2x80x9d technique, or by means of a conducting glue. The conducting glue may be anisotropic so that it conducts current vertically between boards without conducting current laterally between different contact pads.
In the second case, it is advantageous to form depressions to make reservoirs to collect any excess glue during assembly, in the second substrate board before assembly takes place.
If the electrical connections are made by bushings of meltable material, the process may also comprise placement of a dielectric filling material between the first and second substrate boards, the said dielectric material surrounding the bushings made of a meltable material.
Advantageously, in this case it is also possible to form a portion of the tracks intended to receive the bushings of meltable material in a depression in the second board. The depression will then hold the dielectric filling material during assembly.
Furthermore, the depression in the second board can be formed with an upstand arranged outside the areas of the depression in the first board, such that a bottleneck is formed by the upstands of the depressions in the first and second boards. The bottleneck prevents the filling material from spreading out onto the connection strips during assembly of the substrate boards.
Furthermore, at least one component connected to at least one of the conducting tracks can be formed in the second substrate board, and associated with a contact pad on the first board.
The invention also relates to an electronic module comprising:
a first substrate board with at least one electronic component and contact pads connected to the component,
a second substrate board assembled to the first board, the second board comprising conducting tracks electrically connected to the contact pads and extending over a connection strip on the second board that projects beyond the edge of the first board.
This type of module can be made according to the process described above.
When the electronic components are power components, the module may also comprise at least one heat sink fixed to at least one free face of the first and second boards.
The invention also relates to an electronic device comprising a package, contact pins formed in the package and an electronic module like that described above inserted in the package. Conducting tracks of the connection strip are connected by wire to the corresponding contact pins.